It has been common practice for many years to run a continuous reeled pipe (known extensively in the industry as "coil tubing") into a well to perform operations utilising the circulation of treating and cleanout fluids such as water, oil, acid, corrosion inhibitors, hot oil, nitrogen, foam, etc. Coil tubing, being continuous rather than jointed, is run into and out of a well with continuous movement of the tubing through a coil tubing injector.
Coil tubing is frequently used to circulate cleanout fluids through a well for the purpose of eliminating sand bridges, scale, and similar downhole obstructions. Often such obstructions are very difficult and occasionally impossible to remove because of the inability to rotate the coil tubing and drill out such obstructions. These well tubulars vary from unperforated and perforated pipe, large diameter casing, production tubing, and slotted or wire-wrapped well liner. Well tubulars often become plugged or coated with corrosion products, sediments and hydrocarbon deposits. The deposits may consist of silicates, sulphates, sulphide, carbonates, calcium, and organic growth.
It is desirable to perform drilling type operations in wells through use of coil tubing which can be run into and removed from a well quickly in addition to performing the usual operations which require only the circulation of fluids. The same types of well servicing can also be performed with various small diameter work strings. The present invention may be used with such work strings and is not limited to coil tubing.
High pressure fluid jet systems have been used for many years to clean the inside diameter of well tubulars. Examples of such systems are disclosed in the following U.S. Pat. Nos.: 3,720,264, 3,811,499, 3,829,134, 3,850,241, 4,088,191, 4,349,073, 4,441,557, 4,442,899, 4,518,041, 4,919,204, 5,181,576 or 5,337,819.
In U.S. Pat. No. 3,720,264, there is disclosed a jet tool for cleaning a liner. At its one end, the tool carries a bit to provide mechanical centralisation. The blades of the bit are selected to be only slightly less in diameter than the inside diameter of the liner which is to be cleaned.
U.S. Pat. No. 5,337,819 discloses a washing tool for removing internal deposits in tubing parts and components in wells for oil. and gas production. The known tool comprises an actuation sleeve which has lateral dimensions related to the deposits to be removed. The sleeve actuates a valve to discharge a fluid jet through one or more discharge nozzles.
In view of the above cited prior art it is an object of the invention is to provide a fluid jet cleaning tool to remove scale and other deposits from the inside diameter of a well tubular. It is a particular object of the invention to provide a novel stabilising and/or centralising means for such a fluid jet cleaning tool.